That Top-of-the-Food-Chain Feeling

 A flashback to the recent days spent diving at Kingman Reef.

by Gareth Williams

For ten years, I’ve been diving on numerous tropical reefs including those at Fiji, Tonga, Cook Islands, American Samoa, Australia and Vietnam, but only at places like Palmyra Atoll and Kingman Reef can I regularly guarantee having multiple shark encounters on a single dive. In fact, during my first few days diving at these two sites I saw more sharks than I had seen throughout my entire diving career. It’s truly astonishing.

The smaller reef sharks are curious, the grey reefs especially so and can be a little unnerving in large numbers. However, when a larger shark turns up, you are suddenly reminded that the marine environment is not your natural setting and that you are no longer top of the food chain. This large hammerhead (Sphyrna mokarran) came into view at 15m depth on the forereef at Kingman, appearing powerful, yet swimming with such grace. The girth of these sharks gives them a dominating presence and their silvery skin highlights their muscular physique. They were not aggressive, merely curious. Encounters like these are a reminder that it is sharks that should fear us, not the other way around.

Shipwreck Ahoy!

by Linda Wegley, a Ph.D. student in the Rohwer Lab, SDSU

No matter how remote the coral reef, sooner or later some ship is apt to go aground there, leaving a carcass of wood and steel slowly disintegrating on the sea floor. The Line Islands are no exception. Shipwrecks have been documented on Fanning, Palmyra, Starbuck, and Millennium (as well as at several atolls in the nearby Phoenix Islands). The reefs surrounding these shipwrecks decline into a ghastly scene known as a black reef. Here turf algae and cyanobacterial mats flourish and there is a dramatic loss of corals.

In 2009, we investigated a black reef on Millennium Atoll in the Southern Line Islands where an 85 foot steel tug had run aground in 1993 while towing a sailing vessel out through a narrow reef passage. Instead of the 66% live coral cover found elsewhere on Millennium, near the wreck coral cover was reduced to less than 17% of the substrate. Similar declines in coral and increases in turf algae have been observed on black reefs at Fanning and Starbuck.

Different Places, Different Theories

The Hanse Explorer has left Kingman and traveled south to a populated island belonging to the Republic of Kiribati, Fanning Island (Tabuaeran). Like Palmyra, Fanning's topography was dramatically altered, in this case by the British in 1888 who blasted a channel to provide easier access to the lagoon. By 1987 the population had grown to only 450, making this 33 km2 island an attractive destination for the government-promoted relocation of people from the more crowded islands in Kiribati. Current population is about 2500, and growing. The deterioration of the reefs here shows what even that modest number of people can do in a couple of decades.

by Stuart Sandin, head researcher on the Fish Team

Chlororus frontalisWhat I enjoy the most about visiting different coral reefs is the fun of considering the different ecology governing each system. On the steep reefs of Curaçao, I pondered the importance of depth in structuring reef communities, with deeper areas getting less sunlight but more nutrients. In the protected reefs of Caribbean Panama, I considered the importance of water movement (or lack thereof) in determining what species arrive to a reef and how those species may change evolutionarily. And on the heavy reefs of Kingman, I think about what it means to be big.

There are really a lot of big animals on Kingman. When we jump into the water, a few grey reef sharks are right there to greet us in the water column. When we reach the bottom, there are aggregations of red snappers, each measuring about a foot or two long. Gliding along the reef slope are manta rays. Scattered across the bottom are table corals that are two diver lengths in width.

I understand why big animals go away when there is more of a human presence on a coral reef. We have fishing gear targeted to catch larger fish. Anchors dropped on reefs tend to break corals into smaller pieces. In general, it takes time to make large animals, and the human propensity to increase the rate of death for many animals inherently leads to a disproportionate number of smaller, i.e., younger, animals. But there is another important question that we have to answer: why should we care if big animals go away? Are larger animals somehow more valuable in terms of ecology or economics? This is why we just visited Palmyra and Kingman, and why we are comparing these islands to others that have fewer large animals.

Coral Surveys at Kingman Reef

by the Paleo-Benthic Team

Kingman Reef was amazing. The sharks, manta rays, dolphins and large fish thrilled us. Fields of colossal Porites corals, some more than 3 m in diameter, covered the back-reef and patch reefs, while the spaces in between were blanketed by teams of technicolor Tridacna clams. We [the Paleo Benthics] collected core samples from ten Porites colonies scattered around Kingman. In general, the colonies appeared quite healthy, with only a very few patches of partial mortality. Some of them had quite abundant bite-marks from fish and other predators, and several had scars where a crown-of-thorns starfish had munched. The sharks seemed attracted by the sound of the drill but mostly didn’t get uncomfortably close—except one day when a fish escaped from the Fish Team and swam directly over us, accompanied by a squadron of sharks hoping for an easy meal.

Tent Madness

Another photo album from the field, this one sent from Kingman Reef by Benthic Team member Gareth Williams.

One Shipwreck Can Ruin Your Entire Century

by Katie Barott, member of the Microbe Team

As everyone knows, when a ship goes aground on a coral reef, the corals and other benthic critters in its path get crushed. But, unfortunately, in areas like the Line Islands this physical destruction is the least of the damage.

The term "shipwreck" may conjure images of stormy nights of the distant, pre-technological past. The reality is that accidents still happen. Just three years ago, in 2007, a ship ran aground on Kingman. In the intervening years, the reef surrounding the wreck has disintegrated into a murky mess full of dead and dying corals with lots of black algae growing on the bottom. We headed out to the site in the Zodiac. As we descended to investigate the reef near the wreckage, it was as if we had suddenly been transported from Kingman to a different island. Gone was the pink frosting of the crustose coralline algae that help shape the reef, gone were the massive coral colonies, and gone was the clear water and 200 ft visibility. Instead we saw only a few remaining coral colonies—small, many looking diseased—struggling to survive despite the overgrowth of mats of thin filamentous cyanobacteria and algae. I had an eerie feeling as the sharks loomed in and out of view in the murky water.

One Fish, Two Fish

by Stuart Sandin, head researcher on the Fish Team

If you listen to what our colleagues onboard have to say, you'd think we in the Fish Team were a simple bunch. In their eyes, we swim about on the reefs with only the most mundane of equipment—a dive slate and a pencil—and we record the fish that we see. I have even received a copy of Dr Seuss’s One Fish Two Fish Red Fish Blue Fish from Forest’s five year-old daughter as a birthday gift. Thanks for the scientific training manual, Willow!

Yes, we have counted a lot of fish. And yes, we have used simple equipment. But the data collected have been far from simple. As opposed to simply counting all fish to the closest color, we also record the species identity and the size of each individual within our survey area. Given this information, we can rely on established mathematical relationships between length and weight to estimate the weight of each fish counted. Further, based on natural history knowledge about the behavior of each species, we can categorize the fish into functional groups. We typically classify them based on what they eat: algae-eating herbivores, plankton-eating planktivores, crab- (and other invertebrate-) eating omnivores, and the top-dog, fish-eating apex predators.

On Becoming Part of the Food Chain

by Scott Hamilton and Brian Zgliczynski, members of the Fish Team

A few hours after dark, we arrived at Kingman Reef—a U.S. Fish & Wildlife Refuge and Marine National Monument at the northwestern end of the Line Islands chain and arguably one of the most pristine coral reefs remaining on the planet. As the Hanse Explorer turned to enter the mouth of this horseshoe-shaped reef system, we were greeted by jumping schools of needlefish and flying fish illuminated by our bright ship lights. We set anchor and within minutes the needlefish congregated around the ship’s lights, looking for prey. Just as quickly, the apex predators (grey reef sharks) began encircling the boat, looking to prey on unsuspecting needlefish. Over thirty large sharks patrolled nearby, tentative at first—making quick little strikes to gauge the reaction of their prey. For the next several hours we watched the sharks chase and attack needlefish right at the surface of the water. Each successful strike was accompanied by a feeding frenzy as sharks rushed into a roiling mass, fighting over the remains. This exact scene was to recreate itself over the successive three evenings at Kingman, but all we could think about at this moment was that in the morning we would be diving amongst all those sharks as part of the Fish Team.

Night Life at Club King

by Forest Rohwer, head researcher on the Microbe Team

Here at Kingman, sharks—lots of sharks—patrol the waters around the ship at night. Dinner is served, drawn by the lure of the ship's lights. Every few minutes a needlefish makes a poor life choice and enters the killing field. There follows a frantic feeding frenzy, with the fish jumping to escape the snapping swarm. One wrong turn by the fish and its all over. A lot more entertaining than TV. Much of the Halloween party (see previous post) was spent rooting for either the sharks or needlefish.

Observing the feeding frenzy, as well as the noticeably more aggressive behavior of the sharks at dusk, dampens any thoughts of night diving. This means that we know very little about what happens on Kingman Reef at night. To watch the nocturnal life of the reef, Katie Barott and I have been setting up cameras to run remotely. After dark the reef really comes to life with invertebrates (shrimps, sea urchins, crabs, snails, etc.), most of which we never see during the day. Their primary activity seems to be feeding on the crustose coralline algae. Switch between the two photos and see if you can find all of the little creatures that are moving around.

Halloween on Kingman Reef

The scary scene aboard the Hanse Explorer, Halloween night.

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